I think it would largely depend on why the cop pulled you over in the first place. I've been pulled over before for only going a few mph over the speed limit. But I imagine if you were driving like a complete idiot the situation would be more serious.
Then again I've never been in a situation where "weed smoke poured out" of my car when I've encountered the police, so who knows. If you're worried about it than buy a cheap air freshener and roll down your windows.